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Sand and gravel are unconsolidated, granular mineral materials produced by the natural disintegration of rock caused by weathering. The terms sand, gravel, clay and silt relate to grain size rather than composition. Sand is material passing through a number 4 (4.

Slug is a common name for several terrestrial pulmonate and numerous marine gilled species of gastropod molluscs conspicuous by the lack of an exposed shell.

Thrips, order Thysanoptera (Gk for "fringe-wings"), are among the smallest insects, being slender and usually less than 2 mm long.

Acid rain is the wet or dry deposition of acidic substances and their precursors on the Earth's surface. The ongoing industrialization of society has resulted in the increased release of acidic chemicals into the atmosphere.

The tanager (Thraupidae) is a family of small songbirds, possibly comprising as many as 413 species.

The sturgeon is a large, primitive, bony fish of class Actinopterygii, family Acipenseridae. The 4 genera and 24 species live in fresh and coastal waters of the Northern Hemisphere.

Tungsten (W), also called Wolfram, lapis ponderosus or Heavy Stone, is a silver-grey metallic element with the highest melting point of any metal (3410° C). Tungsten has a high density, high strength at elevated temperatures and extreme hardness.

Unlike other mountainous countries such as Switzerland, and despite its size, Canada is not distinguished by well-known tunnels.

Shrimp are decapods ("10-footed") crustacean, differing from other decapods in being adapted for swimming, a fact reflected in the large, laterally compressed abdomen and well-developed pairs of swimming legs.

Sea Urchin, radially symmetrical marine invertebrate. Sea urchins and near relatives, the sand dollars and heart urchins, belong to class Echinoidea of phylum Echinodermata.

Seabirds are those bird species which spend long periods away from land and obtain all or most of their food from the sea while flying, swimming or diving, and occupy all of the world's oceans.

Sponge (Porifera), phylum of bottom-dwelling, attached, aquatic organisms which, as adults, generate vigorous water currents through their porous bodies by action of internal fields of microscopic flagella (whiplike structures).

A spring is a point of natural, concentrated groundwater discharge from soil or rock.

Starfish, or sea star, is a common marine animal found from seashore to ocean depths; 1600 species are known worldwide.

Strawberry, seeBERRIES, CULTIVATED; BERRIES, WILD.

Sparrow is the name given to several unrelated groups of birds. Sparrows are classified in 3 families: Emberizidae, Estrildidae, and Passeridae.

Sphagnum, see MOSS; PEAT; SWAMP, MARSH AND BOG.

Spiraea is a genus of small shrubs of the family Rosaceae (rose). The genus consists of some 70-80 species, as well as many horticultural varieties of garden origin that have resulted from hybridization. Probably the most noteworthy of these hybrids is S.

 Squirrel, common name for family (Sciuridae) of rodents, comprising 262 species, found in North and South America, Eurasia and Africa.

Silica, or silicon dioxide (SiO2), occurs as the MINERAL quartz and is the most abundant mineral of the Earth's crust. It also occurs in the skeletal parts of some animals (eg, certain protozoa) and various plants.